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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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Pressure-induced transient structural change of liquid germanium induced by high-energy picosecond laser pulses

N. Chaoui, J. Siegel, S. M. Wiggins, and J. Solis

Appl. Phys. Lett. 86, 221901 (2005); http://dx.doi.org/10.1063/1.1940117 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2005

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The temporal evolution of the reflectivity of germanium at 514 nm upon irradiation with single high-energy picosecond laser pulses has been measured using a streak camera. It is found that, for a well-defined high fluence range, the reflectivity of the laser-induced molten phase attains a value of 0.85, considerably above the value reported for liquid Ge in thermal equilibrium (0.75). This behavior is consistent with a strong densification of the liquid phase remaining after the explosive vaporization of a thin surface layer. Within the specified fluence interval, this anomalously high reflectivity state is independent of the fluence and lasts tens of nanoseconds. Both characteristics point to the presence of a pressure-induced transient structural change in liquid germanium.
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62.50.-p High-pressure effects in solids and liquids
78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
64.70.F- Liquid-vapor transitions
61.25.-f Studies of specific liquid structures

Ion damage effects from negative deflector plate voltages during the plasma-assisted molecular-beam epitaxy growth of dilute nitrides

Michael M. Oye, Mark A. Wistey, Jason M. Reifsnider, Sumit Agarwal, Terry J. Mattord, Sridhar Govindaraju, Gary A. Hallock, Archie L. Holmes, Seth R. Bank, Homan B. Yuen, and James S. Harris

Appl. Phys. Lett. 86, 221902 (2005); http://dx.doi.org/10.1063/1.1940126 (3 pages) | Cited 5 times

Online Publication Date: 24 May 2005

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We studied the effects of ion damage on the optical properties of dilute nitrides grown by plasma-assisted molecular-beam epitaxy. A dual-grid retarding field ion energy analyzer was used to measure the ion flux and ion energy distribution at the substrate position from an Applied-EPI UniBuilb™ rf plasma cell. These changes were measured as the negative deflector plate voltage varied from 0 to −800 V. The largest ion flux resulted with a −100 V setting, while the greatest ion energies occurred with −200 V. Deflector plate voltages more negative than −300 V resulted in a significant reduction in both the ion flux and ion energy. The damage caused by these ions was determined by measuring the pre- and postanneal photoluminescence properties of Ga0.8In0.2N0.01As0.99 quantum wells. Comparable optical properties were possible with various combinations of ion fluxes and ion energies, which demonstrate how the ion flux and ion energy each impart an individual effect on the sample’s optical properties. An awareness of these effects is crucial because the optical properties of dilute nitrides grown with an improper deflector plate voltage setting can lead to a greater degree of ion damage to the sample.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Critical precipitate size revisited and implications for oxygen precipitation in silicon

Jan Vanhellemont, Olivier De Gryse, and Paul Clauws

Appl. Phys. Lett. 86, 221903 (2005); http://dx.doi.org/10.1063/1.1940140 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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A generalized expression is derived describing the impact of intrinsic point defects and strain on the critical size of spheroidal incoherent precipitates. An important phenomenon that has been neglected so far is the incorporation of intrinsic point defects of the host matrix in the precipitate itself. It is shown that this can have an important impact both on the critical precipitate size, on the amount of emitted intrinsic point defects, and on the precipitated phase itself. The theoretical results are illustrated for the case of oxygen precipitation in silicon.
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81.30.Mh Solid-phase precipitation
61.72.J- Point defects and defect clusters

Phonons in strained In1−xGaxAs/InP epilayers characterized by infrared reflectance

G. Yu, N. L. Rowell, D. J. Lockwood, and P. J. Poole

Appl. Phys. Lett. 86, 221904 (2005); http://dx.doi.org/10.1063/1.1940732 (3 pages) | Cited 5 times

Online Publication Date: 24 May 2005

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Strained In1−xGaxAs epilayers over a wide range of x values from 0.252 to 0.762 have been grown by chemical beam epitaxy on heavily doped InP(100) substrates. The infrared p-polarized reflectivity of these samples has been measured and the first derivative of the reflectance has been analyzed using a specially developed fitting technique. Expressions for the variation of the phonon frequencies with Ga fraction for the InAs-like and GaAs-like modes have been obtained. The present results substantially improve on earlier results obtained from epilayers on semi-insulating substrates having a narrower concentration range around x = 0.468 where In1−xGaxAs is lattice matched to InP.
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81.05.Ea III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Spin-selective optical absorption of singly charged excitons in a quantum dot

Alexander Högele, Martin Kroner, Stefan Seidl, Khaled Karrai, Mete Atatüre, Jan Dreiser, Atac Imamoğlu, Richard J. Warburton, Antonio Badolato, Brian D. Gerardot, and Pierre M. Petroff

Appl. Phys. Lett. 86, 221905 (2005); http://dx.doi.org/10.1063/1.1940733 (3 pages) | Cited 25 times

Online Publication Date: 24 May 2005

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We report high resolution laser absorption spectroscopy of a single InGaAs/GaAs self-assembled quantum dot embedded in a field-effect structure. We show experimentally that the interband optical absorption to the lower Zeeman branch of the singly charged exciton is strongly inhibited due to spin (Pauli) blockade of the optical transition. At high magnetic fields the optical absorption to the upper Zeeman branch dominates the absorption spectrum. We find, however, that the spin blockade is not complete and a 10% leakage remains at high magnetic fields. Applying a gate voltage to empty the dot of its resident electron turns the spin blockade off. This effect is observed at 1.5 K and up to 9 T.
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81.05.Ea III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Fd III-V semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects

Amorphous carbon film growth on Si: Correlation between stress and generation of defects into the substrate

R. S. Brusa, C. Macchi, S. Mariazzi, G. P. Karwasz, N. Laidani, R. Bartali, and M. Anderle

Appl. Phys. Lett. 86, 221906 (2005); http://dx.doi.org/10.1063/1.1940738 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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Amorphous carbon films of several thicknesses were prepared by graphite sputtering on crystalline silicon substrate. The samples were depth profiled with positron annihilation spectroscopy for open-volume measurements and characterized for their residual internal stress. It was found that after film growth the substrate presents vacancy-like defects decorated by oxygen in a layer extending in the substrate by several tens of nanometers beyond the film/Si interface. The width of the defected layer and the decoration of vacancy-like defects are directly and inversely proportional to the measured intensity of the residual stress, respectively. These findings indicate the existence of a relaxation mechanism of the stress in the films that involves deeply the substrate. The decorated vacancy-like defects are suggested to be bounded to dislocations induced in the substrate by the stress relaxation.
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81.05.U- Carbon/carbon-based materials
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters

Photoluminescence characterization of excitonic centers in ZnO epitaxial films

M. Watanabe, M. Sakai, H. Shibata, H. Tampo, P. Fons, K. Iwata, A. Yamada, K. Matsubara, K. Sakurai, S. Ishizuka, S. Niki, K. Nakahara, and H. Takasu

Appl. Phys. Lett. 86, 221907 (2005); http://dx.doi.org/10.1063/1.1940730 (3 pages) | Cited 9 times

Online Publication Date: 24 May 2005

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Photoluminescence properties of nominally undoped ZnO thin films grown by radical-source molecular-beam epitaxy have been investigated as a function of (i) sample growth conditions, (ii) excitation laser power density, and (iii) measurement temperatures. Altogether four excitonic emission peaks were observed at photon energy of 3.3646, 3.3606, 3.3572, and 3.3331 eV, which are tentatively denoted as emission peaks A, D, F, and G, respectively. We have classified the defect types responsible for the emission peaks into the following two groups; (i) D and F, whose responsible defect types are suggested to be residual impurities such as aluminum and indium, respectively, and (ii) A and G, whose responsible defect types are suggested to be intrinsic defects such as oxygen vacancies, interstitial zinc, and extended structural defects particularly for G.
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81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters

Proton irradiation effect on single-wall carbon nanotubes in a poly(3-octylthiophene) matrix

P. P. Neupane, M. O. Manasreh, B. D. Weaver, R. P. Rafaelle, and B. J. Landi

Appl. Phys. Lett. 86, 221908 (2005); http://dx.doi.org/10.1063/1.1940721 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2005

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Proton irradiation effects on interband transitions in single-wall carbon nanotubes matrixed in poly(3-octylthiophene) were investigated. The interband transitions were measured using an optical absorption technique. Two interband transitions were observed, at 0.71 and 1.28 eV in a sample that was subject to 2 MeV proton irradiation to fluences ranging between 5.0×1010 cm−2 and 5.6×1015 cm−2. The optical absorption spectra were collected after cooling the sample to 10 K. The total integrated areas of the two transitions were monitored as a function of proton fluence. The results indicate that proton irradiation to fluences as high as 5.6×1015 cm−2 has little effect on the interband transitions in carbon nanotubes. However, small radiation-related degradation has been observed as judged by the broadening of the interband transition spectra and by the reduction of the radial breathing mode intensity observed by Raman scattering.
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81.07.De Nanotubes
81.05.Qk Reinforced polymers and polymer-based composites
61.80.Jh Ion radiation effects
61.82.Rx Nanocrystalline materials
78.30.-j Infrared and Raman spectra
78.67.Ch Nanotubes

CdTe photoluminescence: Comparison of solar-cell material with surface-modified single crystals

C. R. Corwine, J. R. Sites, T. A. Gessert, W. K. Metzger, P. Dippo, Jingbo Li, A. Duda, and G. Teeter

Appl. Phys. Lett. 86, 221909 (2005); http://dx.doi.org/10.1063/1.1935752 (3 pages) | Cited 4 times

Online Publication Date: 24 May 2005

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Low-temperature photoluminescence (PL) is used to study defect evolution during Cu diffusion into single-crystal CdTe under various atmospheres. PL reveals a zero-order phonon peak at 1.456 eV when Cu-coated CdTe is annealed at 400 °C in an oxidizing atmosphere, but not under other tested conditions. A similar peak is seen in polycrystalline thin-film CdTe samples, which are known to contain copper and oxygen impurities. First-principles band structure calculations determined the likely defect assignment as a transition between a Cui–OTe donor complex and the valence band.
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81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.66.Hf II-VI semiconductors
71.15.-m Methods of electronic structure calculations
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.Mq Oxidation
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
84.60.Jt Photoelectric conversion

Aging effect and origin of deep-level emission in ZnO thin film deposited by pulsed laser deposition

F. K. Shan, G. X. Liu, W. J. Lee, G. H. Lee, I. S. Kim, and B. C. Shin

Appl. Phys. Lett. 86, 221910 (2005); http://dx.doi.org/10.1063/1.1939078 (3 pages) | Cited 59 times

Online Publication Date: 24 May 2005

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ZnO thin films were deposited on sapphire substrates at 400 °C in the pulsed laser deposition (PLD) system. Those thin films showed two emission peaks. One was near band edge emission at around 379 nm; the other was deep-level (DL) emission at around 510 nm. The aging effect on photoluminescence (PL) of the thin film was observed. It was found that the DL emission decreased with time. Post-annealing processes were carried out to find the origin of the DL emission. The thin films were annealed at 800 °C in N2 or O2 ambient gas in a rapid thermal annealing system. An atomic force microscope was used to investigate the surface morphologies of the thin films. The surface roughness of annealed thin film was much smaller than that of the as-deposited one. The transmittance of the annealed thin film decreased much compared with that of the as-deposited thin film. The DL emission of the thin film annealed in N2 increased, and the DL emission of thin film annealed in O2 decreased. The oxygen vacancies instead of zinc interstitials were the main reason for DL emission in ZnO thin films deposited by PLD.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
68.37.Ps Atomic force microscopy (AFM)
71.55.Gs II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters

Compositional stability of hafnium aluminates thin films deposited on Si by atomic layer deposition

C. Driemeier, K. P. Bastos, L. Miotti, I. J. R. Baumvol, N. V. Nguyen, S. Sayan, and C. Krug

Appl. Phys. Lett. 86, 221911 (2005); http://dx.doi.org/10.1063/1.1940130 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2005

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We have used nuclear reaction analyses and Rutherford backscattering spectrometry to investigate quantitatively the compositional stability of hafnium aluminate thin films deposited on Si(001) by atomic layer deposition using HfCl4/H2O and Al(CH3)3/H2O precursors. It was found that increasing Al/Hf deposition cycles ratio leads to increasing oxygen deficiency in the as-deposited films as well as to increasing metal losses (up to ∼ 15%) from the films after rapid thermal annealing at 1000 °C. Furthermore, isotopic substitution experiments, showed that incorporation of oxygen from the gas phase is eased in the cases where deposition conditions failed to supply enough oxygen to complete oxides stoichiometry.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Gold film with gold nitride—A conductor but harder than gold

L. Šiller, N. Peltekis, S. Krishnamurthy, Y. Chao, S. J. Bull, and M. R. C. Hunt

Appl. Phys. Lett. 86, 221912 (2005); http://dx.doi.org/10.1063/1.1941471 (3 pages) | Cited 11 times

Online Publication Date: 24 May 2005

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The formation of surface nitrides on gold films is a particularly attractive proposition, addressing the need to produce harder, but still conductive, gold coatings which reduce wear but avoid the pollution associated with conventional additives. Here we report production of large area gold nitride films on silicon substrates, using reactive ion sputtering and plasma etching, without the need for ultrahigh vacuum. Nanoindentation data show that gold nitride films have a hardness ∼ 50% greater than that of pure gold. These results are important for large-scale applications of gold nitride in coatings and electronics.
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62.20.Qp Friction, tribology, and hardness
81.05.Bx Metals, semimetals, and alloys
81.65.−b
79.60.−i
79.60.Dp Adsorbed layers and thin films
81.15.Cd Deposition by sputtering
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Optimized energy window of He beams for accurate determination of depth in channeling Rutherford backscattering spectrometry

Lin Shao, Y. Q. Wang, X. Zhang, C. J. Wetteland, M. Nastasi, P. E. Thompson, and J. W. Mayer

Appl. Phys. Lett. 86, 221913 (2005); http://dx.doi.org/10.1063/1.1941454 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2005

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We propose a method to improve accurate determination of damage/impurity depth profiles by channeling Rutherford backscattering by using math beams in an energy window of 400–800 keV. This is based on the study of the stopping power of math ions as a function of incident energy along the Si 〈100〉 axis, which shows that the channeling stopping power within the above energy window is close to the random stopping power. Experiments on 100 nm deep Sb-doped Si superlattices show that the approach significantly reduces the error in determining the depth location of Sb, for example, from 8% by using 2-MeV math to 1% by using 600-keV math ions.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
34.50.Bw Energy loss and stopping power
34.50.−s

Ultrathick, low-stress nanostructured diamond films

S. O. Kucheyev, J. Biener, J. W. Tringe, Y. M. Wang, P. B. Mirkarimi, T. van Buuren, S. L. Baker, A. V. Hamza, K. Brühne, and H.-J. Fecht

Appl. Phys. Lett. 86, 221914 (2005); http://dx.doi.org/10.1063/1.1943492 (3 pages) | Cited 6 times

Online Publication Date: 25 May 2005

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We describe a hot-filament chemical vapor deposition process for growing freestanding nanostructured diamond films, ∼ 80 μm thick, with residual tensile stress levels ≲90 MPa. We characterize the film microstructure, mechanical properties, chemical bond distribution, and elemental composition. Results show that our films are nanostructured with columnar grain diameters of ≲150 nm and a highly variable grain length along the growth direction of ∼ 50–1500 nm. These films have a rms surface roughness of ≲200 nm for a 300×400 μm2 scan, which is about one order of magnitude lower than the roughness of typical microcrystalline diamond films of comparable thickness. Soft x-ray absorption near-edge structure (XANES) spectroscopy indicates a large percentage of sp3 bonding in the films, consistent with a high hardness of 66 GPa. Nanoindentation and XANES results are also consistent with a high phase and elemental purity of the films, directly measured by x-ray and electron diffraction, Rutherford backscattering spectrometry, and elastic recoil detection analysis. Cross-sectional transmission electron microscopy reveals a large density of planar defects within the grains, suggesting a high rate of secondary nucleation during film growth. These films represent a new class of smooth, ultrathick nanostructured diamond.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.70.Dm X-ray absorption spectra
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Generation of terahertz monochromatic acoustic phonon pulses by femtosecond optical excitation of a gallium nitride/aluminium nitride superlattice

C. E. Martinez, N. M. Stanton, P. M. Walker, A. J. Kent, S. V. Novikov, and C. T. Foxon

Appl. Phys. Lett. 86, 221915 (2005); http://dx.doi.org/10.1063/1.1941475 (3 pages) | Cited 6 times

Online Publication Date: 25 May 2005

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We describe the generation of pulses of monochromatic acoustic phonons by ultrafast laser excitation of a gallium nitride/aluminium nitride superlattice (SL). The SL response to the optical excitation was studied using femtosecond pump-probe measurements. Superconducting bolometers were used to detect the phonons that leak out of the SL and propagate across the substrate. We see that, for excitation wavelengths around 430 nm, a pronounced enhancement in the longitudinal acoustic phonon signal occurs. The results are consistent with similar measurements using GaAs/AlAs SL’s, where propagating monochromatic phonons were generated under resonant photoexcitation [ Appl. Phys. Lett. 81, 3497 (2002) ].
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.47.-p Spectroscopy of solid state dynamics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Pure-edge dislocation network for strain-relaxed SiGe/Si(001) systems

Akira Sakai, Noriyuki Taoka, Osamu Nakatsuka, Shigeaki Zaima, and Yukio Yasuda

Appl. Phys. Lett. 86, 221916 (2005); http://dx.doi.org/10.1063/1.1943493 (3 pages) | Cited 18 times

Online Publication Date: 26 May 2005

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We have grown strain-relaxed SiGe layers on Si(001) substrates with a pure-edge dislocation network buried at the heterointerface and analyzed dislocation morphology depending on growth conditions. The process employed here consists of pure-Ge film growth on Si(001) and subsequent high temperature annealing for solid-phase intermixing of the Ge film and Si deposited on the top to form a SiGe alloy layer. Transmission electron microscopy revealed morphological changes of shorter pure-edge dislocation segments initially formed at the Ge/Si interface into a network structure consisting of longer and regularly spaced dislocations during post-deposition annealing. The dislocation network was explicitly preserved even after the intermixing of Si and Ge and predominantly contributed to in-plane strain relaxation of the SiGe layer. Applicability of the pure-edge dislocation network to strain-relaxed SiGe buffer layers on Si(001) substrates is discussed.
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68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations

Ultraviolet photovoltage characteristics of SrTiO3−δ/Si heterojunction

Kun Zhao, Yanhong Huang, Qingli Zhou, Kui-Juan Jin, Huibin Lu, Meng He, Bolin Cheng, Yueliang Zhou, Zhenghao Chen, and Guozhen Yang

Appl. Phys. Lett. 86, 221917 (2005); http://dx.doi.org/10.1063/1.1943495 (3 pages) | Cited 37 times

Online Publication Date: 26 May 2005

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A photovoltaic effect is observed in the heterostructure of p-Si/n-SrTiO3−δ (p: hole carrier type, n: electron carrier type). The current–voltage curve exhibits a good rectifying characteristic similar to that of the traditional diode. The junction shows the open circuit voltage of 126 mV/mJ, the short circuit current of 1.78 mA/mJ, and the response time faster than 10 ns for ultraviolet pulsed laser of 25 ns in duration at room temperature, suggesting the promising potential of this junction as a new type of ultrafast ultraviolet detectors with high sensitivity for application.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.40.Ei Rectification
81.05.Cy Elemental semiconductors

Kinetically controlled thin-film growth of layered β- and γ-NaxCoO2 cobaltate

J. Y. Son, Bog G. Kim, and J. H. Cho

Appl. Phys. Lett. 86, 221918 (2005); http://dx.doi.org/10.1063/1.1943498 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2005

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We report growth characteristics of epitaxial β-Na0.6CoO2 and γ-Na0.7CoO2 thin films on (001) sapphire substrates grown by pulsed-laser deposition. Reduction of the deposition rate could change the structure of the NaxCoO2 thin film from a β phase with an island growth mode to a γ phase with a layer-by-layer growth mode. The γ-Na0.7CoO2 thin film exhibits spiral surface growth with multiterraced islands and highly crystallized texture compared to that of the β-Na0.6CoO2 thin film. This heterogeneous epitaxial film growth can give an example of the strain effect of physical properties and growth dynamics of NaxCoO2 as well as the subtle nature of structural change.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Epitaxial growth of CoSi2 in a decanano contact opening on a (100) silicon substrate

Ho-Jung Sun, Young-Jin Lee, Soo-Hyun Kim, Joo-Wan Lee, Ja-Chun Ku, Hyun-Chul Sohn, Jin-Woong Kim, Uisik Kim, and Nak-Kyun Sung

Appl. Phys. Lett. 86, 221919 (2005); http://dx.doi.org/10.1063/1.1943500 (3 pages)

Online Publication Date: 27 May 2005

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The behavior of cobalt silicidation was investigated in a 45-nm-wide contact opening on (100) silicon substrate. A Co film was deposited using sputtering techniques with elongated target-to-wafer spacing and a CoSi2 phase was developed after being annealed using rapid thermal processing at 750 °C for 30 s. It was revealed that the CoSi2 was grown epitaxially both on {111} and (100) Si at the same time, resulting in a faceted single crystal. Type A epitaxy on {111} Si was developed due to the coepitaxial growth. It was suggested that the tendency for the epitaxial growth of CoSi2 was strong in such a highly confined contact opening.
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81.07.Lk Nanocontacts
81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology
61.46.-w Structure of nanoscale materials

Stacking faults in Si nanocrystals

Y. Q. Wang, R. Smirani, and G. G. Ross

Appl. Phys. Lett. 86, 221920 (2005); http://dx.doi.org/10.1063/1.1943501 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2005

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Si nanocrystals (Si nc) were formed by the implantation of Si+ into a SiO2 film on (100) Si, followed by high-temperature annealing. High-resolution transmission electron microscopy has been used to examine the microstructure of the Si nc produced by a high-dose (3×1017 cm−2) implantation. It is shown that there are only stacking-fault (SF) defects in some nanocrystals; while in others the stacking faults (SFs) coexist with twins. Two kinds of SFs, one being an intrinsic SF, the other being an extrinsic SF, have been observed inside the Si nc. More intrinsic SFs have been found in the Si nc, and the possible reasons are discussed. These microstructural defects are expected to play an important role in the light emission from the Si nc.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
68.47.Fg Semiconductor surfaces
61.72.up Other materials
61.72.Nn Stacking faults and other planar or extended defects
81.16.-c Methods of micro- and nanofabrication and processing
68.37.Lp Transmission electron microscopy (TEM)
52.77.Dq Plasma-based ion implantation and deposition
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.82.Rx Nanocrystalline materials

Cu-Si bilayers as storage medium in optical recording

A. E. T. Kuiper, R. J. M. Vullers, D. Pasquariello, and E. P. Naburgh

Appl. Phys. Lett. 86, 221921 (2005); http://dx.doi.org/10.1063/1.1944205 (3 pages) | Cited 12 times

Online Publication Date: 27 May 2005

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Instead of a phase change or a dye layer, a Cu/Si bilayer can be applied as the recording medium in a write-once Blu-ray Disc. The write process basically comprises the formation of a CuSi alloy containing 25–30 at. % Si, while any excess of Si is left behind as unreacted film. Auger analyses of the laser-written layers indicate that recording consists primarily of the diffusion of Si into Cu. The data allow for discrimination between the various models presented in literature for Cu/Si-based recording and to optimize the stack. Very low jitter levels of typically 4% proved to be achievable with equally thick films of Cu and Si as recording medium.
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81.05.Bx Metals, semimetals, and alloys
42.79.Vb Optical storage systems, optical disks
79.60.Bm Clean metal, semiconductor, and insulator surfaces
66.30.-h Diffusion in solids
42.62.-b Laser applications

Theory of compositionally graded ferroelectrics and pyroelectricity

M. Marvan, P. Chvosta, and J. Fousek

Appl. Phys. Lett. 86, 221922 (2005); http://dx.doi.org/10.1063/1.1940729 (3 pages) | Cited 9 times

Online Publication Date: 27 May 2005

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A thermodynamic theory of compositionally graded materials is developed, based on a term in the Landau formula for free energy of the form γPgradc, where P, c, and γ stand for the polarization, the atomic concentration, and a phenomenological coefficient, respectively. The consequence of this term is the following: (1) the original equivalence of two states with spontaneous polarization +PS and −PS is upset and the sample has the tendency to become oriented along one of the originally equivalent directions; (2) an additional polarization is induced. The consequences of the modified free energy for pyroelectricity are discussed.
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77.80.-e Ferroelectricity and antiferroelectricity
77.70.+a Pyroelectric and electrocaloric effects
65.40.G- Other thermodynamical quantities

Relaxation processes in strained Si layers on silicon-germanium- on-insulator substrates

Norio Hirashita, Naoharu Sugiyama, Eiji Toyoda, and Shin-ichi Takagi

Appl. Phys. Lett. 86, 221923 (2005); http://dx.doi.org/10.1063/1.1944208 (3 pages) | Cited 9 times

Online Publication Date: 27 May 2005

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Misfit defects in strained Si layers on silicon-germanium-on-insulator (SGOI) substrates were studied using transmission electron microscopy. With increasing strained-layer thickness, stacking faults with 90° Shockley partial dislocations at strained-Si–SiGe interfaces are found to be increasingly formed in the strained Si layers, extending from the surface to the interface. This fact indicates that generation and glide on {111} planes of the 90° partial dislocations are responsible for the relaxation of the cumulative tensile strain in strained Si layers on SGOI substrates.
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81.05.Cy Elemental semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects
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